Intestinal blood flow is controlled by both feed arteries and microcirculatory resistance vessels in freely moving rats

1. In freely moving rats, intestinal blood flow, aortic blood pressure and blood pressure at the base of mesenteric arcades were measured simultaneously so as to determine the role of feed arteries and of the microcirculation in the control of intestinal vascular resistance. Segmental resistances of feed arteries (R(feed)) and of microcirculatory vessels (R(micro)) were calculated. 2. At rest, R(feed) and R(micro) were 32 and 68%, respectively, of the total intestinal vascular resistance. 3. Injection of noradrenaline (2 mu g I.V.) increased R(feed) by 151% and R(micro) by 243%. Angiotensin II (400 ng I.V.) did not increase R(feed) significantly, but increased R(micro) by 239%. Conversely, serotonin (15 mu g I.V.) increased R(feed) by 414% but did not affect R(micro) significantly. 4. Spontaneous physical activity increased R(feed) by 29% and R(micro) by 39%, while sudden environmental stress increased R(feed) by 116% and R(micro) by 129%. Infused noradrenaline (1 mu g min(-1) I.V.) or adrenaline (0.8 mu g min(-1) I.V.) reduced intestinal flow by 21 and 16%, respectively, while noradrenaline, but not adrenaline, increased intestinal resistances. 5. alpha(1)-Blockade with prazosin (0.1 mg I.V.) reduced R(feed) and R(micro) by 43 and 16%, respectively. Thereafter, environmental stress decreased R(feed) by 24% while R(micro) was unaffected. Intravenous noradrenaline and adrenaline responses were attenuated. 6. We conclude that in freely moving rats, mesenteric feed arteries, as well as microcirculatory vessels, are true resistance vessels, and that both participate in the control of intestinal blood flow.